1. Field of the Invention
This invention relates to a method of forming a microscopic pattern. More particularly, it relates to a method in which a pattern of a photoresist having a high sensitivity to the far-ultraviolet radiation, a high resolution and a high resistance against dry etching is formed and is used to form a microscopic pattern of a desired work piece.
2. Description of the Prior Art
As various semiconductor devices have become high in the density and high in the integration degree in recent years, a method which can readily form a microscopic pattern 0.5-2 .mu.m wide at a high precision has been necessitated.
Heretofore, various patterns of semiconductor devices have been formed by a technology called "photolithography", for which exposure to ultraviolet radiation having wavelengths of approximately 320-500 nm and wet etching employing a liquid etchant have been commonly practised.
However, when the exposure of a photoresist film is performed with the ultraviolet radiation having the wavelengths of 320-500 nm, properties inherent in radiation such as diffraction and interference render it difficult to precisely form the microscopic pattern having the width of 0.5-2 .mu.m.
When the etching is performed by the wet etching employing the liquid etchant, the precision of formation of a pattern lowers due to the side etching etc. It is therefore difficult to precisely form the microscopic pattern.
Since, as thus far described, the microscopic pattern cannot be formed at the high precision with the hitherto conventional method, there has been proposed a method which employs for the exposure, ultraviolet radiation having wavelengths of approximately 200-320 nm shorter than the wavelengths of the aforecited ultraviolet radiation (such ultraviolet radiation of the shorter wavelengths shall be written "far-ultraviolet radiation" in this specification) and which employs for the etching, various dry etchings employing no liquid etchant.
This measure eliminates both the influences of the diffraction and interference of the radiation ascribable to the use of the ultraviolet radiation of the longer wavelengths for the exposure and the lowering of the precision due to the side etching in the etching step, so that the formation of the microscopic pattern ought to be possible.
However, it has hitherto been impossible to achieve sufficiently good results because of nonexistence of any photoresist suitable for both the exposure to the far-ultraviolet radiation and the dry etching.
By way of example, polymethyl methacrylate (abbreviated to "PMMA") and polymethyl isopropenyl ketone (abbreviated to "PMIPK") are usually used as photoresists for the far-ultraviolet radiation. Although these photoresists are excellent in point of the resolution, they have an insufficient sensitivity to the far-ultraviolet radiation and require a long time for the exposure, and moreover, they are insufficient in point of the resistance against the dry etching and incur a great damage of a resist pattern during the dry etching step. It has therefore been difficult to put them into practical use. In particular, it is a fatal disadvantage in practical use that the resistance against the dry etching is low.